In recent years, portable electronic devices such as portable audio devices, mobile phones, and laptop computers are widely prevalent, and various secondary batteries are being used as power supplies of such portable electronic devices. Moreover, there are much greater needs for large-capacity secondary batteries than for portable electronic devices. For example, from an energy saving standpoint, or from a standpoint of reducing the discharged amount of carbon dioxide, among automobiles incorporating conventional internal combustion engines, hybrid vehicles are gaining prevalence in which an electricity-based driving force is also utilized. Therefore, regardless of the purpose, secondary batteries having improved characteristics, e.g., output power, capacity, cyclic characteristics, are needed.
Since a secondary battery stores electric charge through an oxidation-reduction reaction, the aforementioned characteristics of the secondary battery are greatly affected by a substance which reversibly undergoes oxidation-reduction reactions, i.e., an electricity storage material which stores electric charge. In conventional secondary batteries, metals, carbon, inorganic compounds, and the like have been used as electricity storage materials. For example, in the case of lithium secondary batteries which are currently in wide use, metal oxide, graphite, and the like have been used as a positive-electrode active substance and a negative-electrode active substance, which are electricity storage materials.
Instead of these inorganic materials, organic compounds are being studied for use as electricity storage materials. As compared to inorganic compounds, organic compounds have established synthesis methods, thus making it relatively easy to synthesize compounds having new molecular structures as designed. Therefore, it is considered that using organic compounds as active substances makes it possible to realize active substance with various characteristics based on molecular designs.
Moreover, since organic compounds are lighter in weight than metals, a light-weight secondary battery can be realized when a secondary battery is constructed by using electricity storage materials composed of organic compounds. Therefore, for example, they can be considered as suitable for secondary batteries of hybrid vehicles, which do not need to have a high charge density but are required to be light-weighted. Use of capacitors as electricity storage devices for hybrid vehicles is also under study. The above advantages will also be available when electricity storage materials composed of organic compounds are used for a capacitor that utilizes chemical reactions.
In Patent Documents 1 and 2, the inventors of the present invention have proposed an organic compound having a π electron conjugated cloud, as a new electricity storage material which is expected to realize rapid charging and discharging, and revealed its reaction mechanism.
Such an organic compound having a π electron conjugated cloud can be synthesized either as a low-molecular-weight compound or as a polymer compound. In the case where an organic compound having a π electron conjugated cloud is used for an electricity storage device such as a secondary battery, since a nonaqueous solvent is used as an electrolyte solution, it is preferable to use an organic compound having a π electron conjugated cloud in the form of a polymer compound, in order to suppress elution into the electrolyte solution and improve the characteristics of the electricity storage device.
In Patent Document 3, the inventors of the present invention have proposed using, for an electricity storage device, a polymer compound which includes a plurality of organic compound sites having a π electron conjugated cloud. For example, they have disclosed a polymer compound which is obtained by allowing an organic compound site having π electron conjugated cloud to bind to a polymer compound having a polyacetylene or polymethylmethacrylate chain as a main chain. Moreover, they have disclosed a polymer compound which is obtained through a dehydration condensation of a side chain having carboxytetrathiafulvalene onto a main chain of polyvinyl alcohol.